This application relies for priority upon Korean Patent Application No. 2001-18557, filed on Apr. 4, 2002, the contents of which are herein incorporated by reference in their entirety.
1. Field of the Invention
The present invention relates to a semiconductor package manufacturing apparatus and, more particularly, to a tablet detecting system for a molding tablet supplying apparatus.
2. Description of the Related Art
Semiconductor products are manufactured in general through many processes, i.e., wafer fabrication, EDS (electrical die-sorting), package assembly and test processes. The package assembly process includes a wafer sawing process, a die attaching process, a wire bonding process, a molding process, and a lead trimming/forming process.
In the molding process, wire-bonded semiconductor chips are encapsulated with molding resin such as epoxy compound. The molding resin is supplied to a molding apparatus in the form of solid tablets. The tablets are heated, melted and injected into the mold dies of the molding apparatus, and then hardened to form a package body.
An automated apparatus supplies the molding tablets to the molding apparatus. A conventional tablet supplying apparatus is shown in FIG. 1. As shown in FIG. 1, the conventional tablet supplying apparatus 10 includes a storing unit 20, an aligning unit 30, a transfer unit 40 and a loader unit 50.
The storing unit 20 stores the tablets 12 and discharges the tablets 12 through an exit slide 22. Typically, the tablet 12 has a cylindrical shape. The aligning unit 30 arranges the tablets 12 in an upright posture. The tablet 12 discharged from the storing unit 20 drops to a conical plane 32 of the aligning unit 30. The peripheral edge of the conical plane 32 connects with a curved road 34a. The tablets 12 on the conical plane 32 gather around the peripheral edge of the conical plane 32 and then move along the curved road 34a by a vibrating act of the aligning unit 30. On the curved road 34a, a height sorter 36a and a diameter sorter 36b are positioned to sort out bigger tablets 12. That is, the sorters 36a and 36b stop tablets 12 larger than standard height and diameter. Only tablets 12 of standard size or smaller can move to a straight road 34b. 
The transfer unit 40 transfers one by one the tablets 12 from the end of the straight road 34b to the loader unit 50. The transfer unit 40 has a transfer rod 42, an air cylinder 44 and a transfer plate 46. The transfer rod 42 has a grasp groove 42a and the transfer plate 46 has a drop hole 46a. After the tablet 12 discharged from the straight road 34b is caught in the grasp groove 42a, the air cylinder 44 pushes the transfer rod 42 toward the drop hole 46a. When the grasp groove 42a reaches the drop hole 46a, the tablet 12 in the grasp groove 42a falls through the drop hole 46a to the loader unit 50 under the transfer plate 46.
A loader block 51 of the loader unit 50 has a lateral hollow 51a and plural receiving holes 51b. A lifting plate 52 is placed in the lateral hollow 51a and plural lifting pins 53 are formed on the lifting plate 52. Each lifting pin 53 is inserted into the receiving hole 51b. The lifting plate 52 can move up and down by the rotation of a screw rod 55 driven by a motor 54. The tablet 12 supplied through the drop hole 46a stays in the receiving hole 51b, while the lifting pin 53 supports the bottom of the tablet 12. Thereafter, the loader unit 50 moves to the molding apparatus (not shown) and the lifting pin 53 pushes up the tablet 12 in the receiving hole 51b by the rising of the lifting plate 52.
As described above, tablets 12 exceeding the standard size are unacceptable and sorted out by both the height sorter 36a and the diameter sorter 36b. However, another unacceptable tablets 12 below the standard size pass through the sorters 36a and 36b. Unfortunately, when the smaller tablets 12 are used for the molding process, the package body is incompletely filled. In these situations, the package bodies include voids after cooling because the culls are thinner than the standard thickness. Additionally, poor packages formed from unacceptable tablets are more common in small packages like the ball grid array (BGA) packages.
For the above reasons, the conventional tablet supplying apparatus 10 further uses a tablet detecting system 60 to discover the existence of unacceptable tablets before supplying the tablets 12 to the molding apparatus. As illustrated in FIGS. 1 and 2, the conventional detecting system 60 includes movable rods 62 and a sensor 64. When the loader unit 50 is positioned under the detecting system 60, the movable rods 62 are inserted into the receiving holes 51b of the loader unit 50. The movable rods 62 can freely move up and down. As depicted in FIG. 2, if the tablet 12 exists in the receiving hole 51b, the movable rod 62 moves upward just as high as the tablet 12. Further, the sensor 64 senses the existence of the movable rod 62 at a position equivalent to the height of the standard-sized tablet 12. Therefore, if no tablet or a smaller tablet exists in the receiving hole 51b, the movable rod 62 does not reach the position of the sensor 64 and the tablets are determined to be unacceptable.
The conventional tablet detecting system has a difficulty in precisely distinguishing unacceptable tablets that are very similar in size to the standard tablets. Considering a tendency toward smaller packages, a minute difference in size of the tablet is becoming a more important factor in reliable molding process. Therefore, a precise detection system for ascertaining minute size differences of the tablets is required. Furthermore, a sensor of the conventional detecting system often operates erroneously due to impurities such as tablet particles.
The present invention provides a tablet detecting system, which can ascertain whether a tablet exists in a receiving hole of a loader unit used for a molding tablet supplying apparatus or, if exists, whether the tablet has a standard size, by using a mechanical contact manner.
The tablet detecting system of the present invention comprises a push rod, a contact head, an insulation plate, a conductive assembly and a control unit. The push rod is inserted into the receiving hole and moves upward just as high as the tablet. The contact head is formed on a top of the push rod and made of electrically conductive material. The insulation plate is located over the contact head. The conductive assembly is formed in the insulation plate and made of electrically conductive material. The control unit is electrically connected to the conductive assembly. In particular, when the tablet in the receiving hole has a standard size, the contact head mechanically touches the conductive assembly and gives electrical connection to the conductive assembly, and the control unit senses the electrical connection.
In the tablet detecting system of the present invention, the conductive assembly may include a pair of conductive pads formed separately on a bottom surface of the insulation plate. Alternatively, the conductive assembly may include a pair of cylindrical bodies each formed in the insulation plate and spaced apart from each other, a pair of plungers each inserted into the cylindrical body, and a pair of springs each interposed between the cylindrical body and the plunger so that the plunger protrudes downward from the insulation plate. The contact head may have a size enough to simultaneously touch the pair of conductive pads or the pair of plungers.